With watercraft instruments of this kind it is known to attach the transparent front instrument glass to the instrument body with the aid of a frame, provided with a bayonet-fitting which coacts with the instrument body. The frame serves as an attachment means and also as a decoration and one and the same instrument can be provided with different frames for fitting the instrument to different installations, e.g. different types of engine. When necessary, one type of frame can be exchanged for another, e.g. if the instrument is moved to another panel.
It must be possible to fit certain types of watercraft instruments, or gauges, into an open recess in a watercraft, which means that the instrument must be watertight and consequently that there must be a close fit between frame, glass and instrument body. Furthermore, a great deal of accuracy is required when fitting the parts together. If the parts are not fitted together correctly it is possible that moisture will penetrate into the instrument and damage the same.